defmodule Microwaveprop.Propagation.CalibrationTest do
  use ExUnit.Case, async: true

  alias Microwaveprop.Propagation.Calibration

  describe "spearman/2" do
    test "perfect monotonic correlation is 1.0" do
      assert_in_delta Calibration.spearman([1, 2, 3, 4, 5], [10, 20, 30, 40, 50]), 1.0, 1.0e-9
    end

    test "perfect inverse correlation is -1.0" do
      assert_in_delta Calibration.spearman([1, 2, 3, 4, 5], [50, 40, 30, 20, 10]), -1.0, 1.0e-9
    end

    test "uncorrelated input lands near zero" do
      xs = Enum.to_list(1..100)
      # constant ys has zero variance; function returns 0.0 by convention.
      ys = List.duplicate(42, 100)
      assert Calibration.spearman(xs, ys) == 0.0
    end

    test "returns nil for fewer than 3 pairs" do
      assert Calibration.spearman([1], [1]) == nil
      assert Calibration.spearman([1, 2], [3, 4]) == nil
    end
  end

  describe "rmse/2" do
    test "zero for identical lists" do
      assert Calibration.rmse([1, 2, 3], [1, 2, 3]) == 0.0
    end
  end
end